JPH06347795A - Liquid crystal display element and its production - Google Patents

Abstract

PURPOSE:To provide a process or omproving the orientation reliabillity of the liquid rystal of the conventional liquid crystal display element and applying a pretilt having high reliability and good uniformity to the orientation of the liquid crystal. CONSTITUTION:The high-molecular precursors dissolved in the liquid crystal are superposed on the first oriented layers 3, 6 formed on substrates 1, 8 with electrodes 2, 7 to form the second oriented layer 4, 5. The pretilt is freely settable by impressing an external field to the element at this time. The long- term reliability of the liquid crystal orientation state, the long-term stability of the pretilt angle and the uniformity of the orientation state are improved. The display of a large capacity which is extremely bright and has a good contrast is inexpensively produced even in the display element formed by using the ferroelectric liquid crystal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a liquid crystal display device used in information equipment, televisions, various electronic bulletin boards, etc., and more particularly to a method for manufacturing a liquid crystal alignment layer.

[0002]

2. Description of the Related Art In a conventionally used TN (twisted nematic) type liquid crystal display element, a method of rubbing the surface in contact with the liquid crystal with a cloth or the like is used in order to orient the liquid crystal in advance (M Schadt and W.D.
Helfrich: Appl. Phys. Lett. ，
18 (1971) 127).

In STN (Super Twisted Nematic) type liquid crystal display elements, pretilt is preliminarily generated in the alignment of the liquid crystal in order to increase the capacity of the display (TJ Schcher and J. Nehri).
ng: Appl. Phys. Lett. , 45 (198
4) 1021, etc., see FIG. 6).

In an SH (super homeotropic) type liquid crystal display element having a wide viewing angle, a liquid crystal having a negative dielectric anisotropy is used, and the liquid crystal is preliminarily in a vertical alignment state slightly tilted, and the liquid crystal is aligned by applying an electric field. The state is a horizontal orientation state (H. Schadt: SID '82 Diges
t (1982) 244). The above is to visualize the electric field response of the element by sandwiching the element with a polarizing plate. However, by including dichroic dye in the liquid crystal, a mode in which the electric field response of the element can be recognized without using the polarizing plate has also been developed. (GH Heilmeier and LA Za
noni: Appl. Phys. Lett. , 13 (1
968) 91). In this mode, since no polarizing plate is used, there is a possibility of displaying paper white.

A display element using a ferroelectric liquid crystal having a memory property that enables a large capacity display has been extremely actively developed for one period. The products that are currently being commercialized are products that have been subjected to a conventional horizontal alignment treatment. However, since the so-called opening angle between the bistable states of the ferroelectric liquid crystal is extremely narrow, the display is dark and the contrast is poor. Therefore, an attempt has been made to increase the opening angle by inclining the orientation of the liquid crystal by using the oblique evaporation method or the like (12th Liquid Crystal Symposium Proceedings, 1st F12, page 32, or J.
apan Display '86 Proceedings 12, 3
464 pages).

Further, as for the alignment treatment technique for providing a pretilt, a conventional oblique vapor deposition method (Japanese Patent Publication No. 63-3216) is used.
2), a method using an alignment film (JP-A-04-70812)
However, there were few methods that could realize a highly reliable and accurate high pretilt angle. Recently, a method has been devised in which a desired pretilt can be realized by using a composite of a low molecular weight liquid crystal and a high molecular weight liquid crystal as an alignment film (JP-A-4-234018, etc.).

[0007]

However, the long-term reliability of the alignment is poor in the prior art, and particularly in the high pretilt alignment treatment used for STN type liquid crystal display devices, the long-term reliability or the uniformity inside the display device is a problem. was there. Further, even in the method of using a composite of a low-molecular liquid crystal and a high-molecular liquid crystal as an alignment film, it is not suitable for mass production because it is necessary to previously form an alignment film containing liquid crystal on the substrate, and an accurate pretilt is applied to the entire display screen. There was a problem that it was extremely difficult to achieve uniform uniformity. Further, even in the mode using the ferroelectric liquid crystal, there is a problem that it is extremely difficult to realize accurate pretilt, uniformity and reliability because the oblique vapor deposition method is used.

Therefore, the object of the present invention is TN
Type and horizontal alignment guest-host liquid crystal display device, STN type, SH type,
In the vertically aligned guest-host type and ferroelectric liquid crystal type liquid crystal display devices, accurate and uniform pretilt and sufficient long-term reliability are realized. It is also an object of the present invention to provide a method of alignment treatment with favorable mass productivity.

[0009]

According to the method of manufacturing a liquid crystal display element of the present invention, in the liquid crystal display element, the surface of two substrates sandwiching the liquid crystal is subjected to an alignment treatment for aligning the liquid crystal. Has a first alignment layer formed in advance,
Further, a second alignment layer is formed thereon by polymerizing a polymer precursor previously mixed in the liquid crystal. Further, when forming the second alignment layer,
The polymer precursor is polymerized while applying an external field to the liquid crystal layer so that the liquid crystal layer produces a desired pretilt. The external field is an electric field or a magnetic field. In addition, the first alignment layer has a vertical alignment force, a horizontal alignment force, or an alignment force that causes pretilt. Further, it is characterized in that an ultraviolet ray, an electron beam or visible light is used to polymerize the polymer precursor. Further, it is characterized in that a substance that absorbs ultraviolet rays, electron beams or visible light is mixed in the liquid crystal. Hereinafter, the details of the present invention will be shown in Examples.

[0010]

【Example】

Example 1 This example shows an example in which the present invention is applied to a normal STN type liquid crystal display element. FIG. 1 is a simple view showing a part of a cross section of an STN type liquid crystal display device of this embodiment. First, a method of manufacturing an empty panel for enclosing a liquid crystal will be described. Electrodes 2 and 7 of two substrates 1 and 8 with electrodes
The first alignment layers 3 and 6 were subjected to horizontal alignment treatment on the surface of, and the two substrates were combined so that the treatment direction was 270 ° twist, and fixed so that the gap was about 5 μm. Next, the liquid crystal 9 is sealed in this gap. This liquid crystal will be described. The liquid crystal was mixed with SS5004 (manufactured by Chisso Corporation) and CB15 as a chiral component so that the helical pitch of the liquid crystal was 4/3 times the thickness of the liquid crystal layer.
Further, 0.5% of biphenyl methacrylate was mixed with this liquid crystal as a polymer precursor for forming the second alignment layers 4 and 5. This mixture was enclosed in the above empty panel and irradiated with ultraviolet rays while applying an electric field so that the tilt angle of the liquid crystal was about 20 degrees in the liquid crystal phase. As a result, the second alignment layers 4 and 5 having irregularities as shown in FIG. 1 were formed on the substrate surface. A polarizing plate was attached to the front and back of this display element to complete the display. The liquid crystal display device thus produced was left at 70 ° C. for 500 hours, but no disorder of alignment occurred. Moreover, no change with time was observed even when the pretilt of the liquid crystal was measured without an electric field. Since the surface shape is larger than that of the first alignment layer and also includes the particle shape, it is considered that the alignment force is strong and the change over time does not easily occur.

When the light used for polymerization is ultraviolet light, it can be used with high or low intensity, but it is 10 mW / cm.
When it is 2 or less, the polymer precursor is sufficiently polymerized. The wavelength is preferably about 300 nm to 400 nm. 300 nm
When the wavelength is shorter, it is treated like an electron beam. 40
When the wavelength is longer than 0 nm, it is treated in the same manner as visible light. When using an electron beam, it is necessary to make the substrate sufficiently thin so that the electron beam can reach the inside. The strength was similar to that of ultraviolet rays and was sufficiently polymerized. Further, depending on the polymer precursor, or by using a sensitizer, it is possible to polymerize with visible light.

When the light used for polymerization is irradiated from both sides of the display element, the amount of polymer attached to the surface of the substrate increases and the amount of polymer remaining in the liquid crystal decreases accordingly, so that the haze when an electric field is applied is reduced. And the contrast is improved.
Of course, the polymer precursor is sufficiently polymerized even by irradiation from one side.

When an ultraviolet absorber is added to the liquid crystal, polymerization occurs only in the vicinity of the electrode surface, so that the amount of polymer remaining in the liquid crystal is further reduced, haze is reduced, and contrast is improved. As the ultraviolet absorber, for example, an ultraviolet absorber having a small sensitizing action such as anthracene or coronene is preferable.

As the polymer precursor to be used, in addition to the methacrylate type as shown here, an acrylate type, an epoxy type and the like can be similarly used. As for the form of the compound, if it is too long and slender, a polymer lacking in rigidity is generated, and therefore it is not useful as an alignment layer. If possible, a rigid molecular shape with an aromatic ring connected is preferable. The birefringence of the polymer precursor should be small. A thermosetting resin may be used in addition to the photocurable resin. At that time, only heating is required for polymerization. The content of the polymer precursor in the liquid crystal is preferably 4% or less. When it is more than this, when an electric field is applied, haze occurs between the polymer and liquid crystal present inside, and light scattering occurs.

The same effect was obtained even when a magnetic field was applied without using an electric field in order to give a pretilt alignment force to the second alignment layer. In addition, without using an external field such as an electric field or a magnetic field, the alignment treatment having the conventional pretilt alignment force is performed to irradiate the polymer precursor by irradiating light such as ultraviolet rays during pretilt alignment after encapsulating the liquid crystal. The same effect was obtained by polymerizing to form the second alignment layer.

Liquid crystal, chiral component, alignment treatment in first alignment layer, thickness of liquid crystal layer, substrate, electrode, polarizing plate, etc. S
The conventional technology can be directly applied to the elements constituting the TN (or SBE, OMI, etc.) mode.

Example 2 In this example, an example in which the present invention is applied to a case in which a liquid crystal having a negative dielectric anisotropy is combined with a panel in which a vertical alignment treatment is performed will be described. FIG. 2 is a view briefly showing a partial cross section of the liquid crystal display element of the present embodiment. First, a method of manufacturing an empty panel for enclosing a liquid crystal will be described. The electrode surfaces of the substrates 1 and 8 with the two electrodes 2 and 7 were subjected to vertical alignment treatment as the first alignment layers 3 and 6, and the surfaces were lightly rubbed in one direction (this treatment is not always necessary). . The two substrates were combined and fixed so that the gap was about 5 μm. Next, the liquid crystal 9 is sealed between the electrodes. This liquid crystal will be described. The second liquid crystal is RDP00775 (made by Rodick)
1% of nonyl biphenyl methacrylate was mixed as a polymer precursor for forming the alignment layer. This mixture was sealed in the above empty panel and irradiated with ultraviolet rays in a state in which the liquid crystal phase was slightly inclined and vertically aligned. As a result,
The second alignment layers 4 and 5 having the unevenness as shown in 1) were formed on the substrate surface. If the rubbing is not performed in one direction after the vertical alignment treatment is performed as the first alignment layer, the irregularities of the second alignment layer are oriented in the vertical direction with respect to the substrate. A polarizing plate was attached to the front and back of this display element to complete the display. The liquid crystal display device thus produced was left at 70 ° C. for 500 hours, but no disorder of alignment occurred. Moreover, no change with time was observed when the tilt angle of the liquid crystal was measured without an electric field. Since the surface shape is larger than that of the first alignment layer and also includes the particle shape, it is considered that the alignment force is strong and the change over time does not easily occur.

When the light used for polymerization is ultraviolet light, it can be used with strong or weak intensity, but it is 10 mW / cm.
When it is 2 or less, the polymer precursor is sufficiently polymerized. The wavelength is preferably about 300 nm to 400 nm. 300 nm
When the wavelength is shorter, it is treated like an electron beam. 40
When the wavelength is longer than 0 nm, it is treated in the same manner as visible light. When using an electron beam, it is necessary to make the substrate sufficiently thin so that the electron beam can reach the inside. The strength was similar to that of ultraviolet rays and was sufficiently polymerized. Further, depending on the polymer precursor, or by using a sensitizer, it is possible to polymerize with visible light.

When the light used for polymerization is irradiated from both sides of the display element, the amount of the polymer attached to the surface of the substrate increases and the amount of the polymer remaining in the liquid crystal decreases accordingly, so that the haze when an electric field is applied is reduced. And the contrast is improved.
Of course, the polymer precursor is sufficiently polymerized even by irradiation from one side.

When an ultraviolet absorber is added to the liquid crystal, polymerization occurs only near the surface of the electrode, so that the amount of polymer remaining in the liquid crystal is further reduced, haze is reduced, and contrast is improved. As the ultraviolet absorber, for example, an ultraviolet absorber having a small sensitizing action such as anthracene or coronene is preferable.

As the polymer precursor to be used, in addition to the methacrylate type as shown here, an acrylate type, an epoxy type and the like can be similarly used. A thermosetting resin may be used in addition to the photocurable resin. At that time, only heating is required for polymerization.

The conventional techniques can be applied to the elements constituting the SH mode, such as liquid crystal, chiral component, alignment treatment in the first alignment layer, substrate, electrode, and polarizing plate.

Example 3 In this example, a polarizing plate is not used in Example 2 but the dichroic dye 10 is mixed instead. FIG. 3 is a view briefly showing a partial cross section of the liquid crystal display element of the present embodiment. The basic device manufacturing method is the same as that of the second embodiment. Liquid crystal dichroic dye S-
The difference is that 344 (manufactured by Mitsui Toatsu Dye Co., Ltd.) was mixed at 2%. As a result, it was possible to manufacture a display element which was colored by applying an electric field and became transparent by removing the electric field. Regarding the reliability of orientation, this display element was left at 70 ° C. for 500 hours, but no disorder of orientation occurred. Moreover, no change with time was observed when the tilt angle of the liquid crystal was measured without an electric field.

The conventional techniques can be applied to the components constituting the guest-host type vertical alignment mode such as liquid crystal, dichroic dye, alignment treatment in the first alignment layer, substrate and electrodes.

(Embodiment 4) This embodiment shows an example in which the present invention is applied to a normal TN mode. FIG. 4 is a simple view showing a partial cross section of the liquid crystal display element of this embodiment. First, a method of manufacturing an empty panel for enclosing the liquid crystal 9 will be described. Firstly on the electrode surface of the substrates 1 and 8 with the two electrodes 2 and 7.
The alignment layers 3 and 6 were subjected to horizontal alignment treatment, and the two substrates were combined so that the treatment direction was twisted by 90 degrees, and fixed so that the gap was about 7 μm. Next, the liquid crystal 9 is sealed between the electrodes. This liquid crystal will be described. The liquid crystal was mixed with SS5004 (manufactured by Chisso Corporation) and CB15 as a chiral component so that the helical pitch of the liquid crystal was 4 times or more the thickness of the liquid crystal layer. Furthermore, 1.5% of benzoyloxyphenyl acrylate was mixed with this liquid crystal as a polymer precursor for forming the second alignment layer. This mixture was enclosed in the above empty panel and irradiated with ultraviolet rays in the liquid crystal phase. As a result, the second alignment layers 4 and 5 having irregularities as shown in FIG. 4 were formed on the substrate surface. A polarizing plate was attached to the front and back of this display element to complete the display. The liquid crystal display device thus produced was left at 70 ° C. for 500 hours, but no disorder of alignment occurred. Since the surface shape is larger than that of the first alignment layer and also includes the particle shape, it is considered that the alignment force is strong and the change over time does not easily occur.

The conditions of Example 1 can be used for the polymerization conditions, additives during polymerization, and polymer precursors.

Liquid crystal, chiral component, alignment treatment in first alignment layer, thickness of liquid crystal layer, substrate, electrode, polarizing plate, etc. T
The conventional technology can be directly applied to the elements constituting the N mode.

In this embodiment, by mixing a dichroic dye in the liquid crystal, it is possible to manufacture a display element which is transparent when an electric field is applied and which is colored in a dye color when no electric field is applied. Also in this case, the long-term reliability in orientation was improved.

(Embodiment 5) This embodiment shows an example in which the present invention is applied to a liquid crystal display device using a ferroelectric liquid crystal. FIG. 5 is a simple cross section showing a partial cross section of the liquid crystal display element of the present embodiment. The surfaces of the substrates 1 and 8 with the two electrodes 2 and 7 were subjected to horizontal alignment treatment as a first alignment layer and bonded to each other so that the gap was 2.2 μm and the rubbing directions were overlapped. In this gap, as a liquid crystal, ZLI made by Merck Ltd.
3488 was filled with a mixture of 0.2% of a polymer precursor biphenyl acrylate for forming a second alignment layer. The panel is then heated to 100 ° C and then 80 ° C.
Slowly cools down to 2 pretilts in the cholesteric phase
An electric field is applied so that the temperature becomes 0 degree, and in this state, ultraviolet rays are radiated from both sides of the panel and then gradually cooled to room temperature.
A second alignment layer as shown in 1 was formed. In the liquid crystal display element thus obtained, the opening angle between the bistable states of the liquid crystal is close to 45 degrees, and when the electro-optical characteristics were measured by sandwiching it with a polarizing plate, a brightness almost equal to the transmittance of the polarizing plate was obtained. The contrast was 50: 1 or more. In addition, the reliability of the alignment state was high, and no change in the alignment was observed even when left at 50 ° C. for 200 hours. Since the surface shape is larger than that of the first alignment layer and also includes the particle shape, it is considered that the alignment force is strong and the change over time does not easily occur.

When setting the pretilt, the electric field may be arbitrarily adjusted so that the liquid crystal has a desired pretilt in the cholesteric phase or the nematic phase.

The liquid crystal used in this embodiment must be a ferroelectric liquid crystal in the operating temperature range and have a cholesteric phase or a nematic phase in the temperature range where the second alignment layer is formed. However, since a second orientation phase can be formed in a phase that responds when a strong external field is applied, such as the smectic A phase, it suffices to have a phase similar to this.

The thickness of the liquid crystal layer is decided in consideration of the size of the pretilt and the bistability, and cannot be decided unconditionally. However, usually 1.5 to 2.5μ
If it is between m, it can be used practically.

As the polymer precursor forming the second alignment layer, any of those shown in the previous examples can be used.

The conventional technique can be applied as it is to the components constituting the mode using the ferroelectric liquid crystal such as the alignment treatment in the first alignment layer, the substrate, the electrode and the polarizing plate.

[0035]

As described above, according to the present invention, the second alignment layer is formed by a very simple method in almost all the liquid crystal display elements that have been developed so far, whereby the long-term reliability of the liquid crystal alignment state, The long-term stability of the pretilt angle and the uniformity of the alignment state could be improved. By using the present invention, it is possible to realize an SBE type display element that has not been put into practical use because of poor alignment reliability in the related art, and it is possible to further improve the display performance. Also in the display device using the ferroelectric liquid crystal, since the orthorhombic alignment can be realized by a very inexpensive method, it has become possible to inexpensively supply a large-capacity display with extremely bright and good contrast. .

[Brief description of drawings]

FIG. 1 is a view briefly showing a partial cross section of a liquid crystal display element of Example 1.

FIG. 2 is a diagram simply showing a partial cross section of a liquid crystal display element of Example 2.

FIG. 3 is a view briefly showing a partial cross section of a liquid crystal display element of Example 3.

FIG. 4 is a diagram simply showing a partial cross section of a liquid crystal display element of Example 4.

FIG. 5 is a diagram simply showing a partial cross section of a liquid crystal display element of Example 5.

FIG. 6 is a view briefly showing a partial cross section of a conventional STN type liquid crystal display element.

[Explanation of symbols]

 1 Substrate 2 Electrode 3 First Alignment Layer 4 Second Alignment Layer 5 Second Alignment Layer 6 First Alignment Layer 7 Electrode 8 Substrate 9 Liquid Crystal 10 2 Chromatic Dye 11 Ferroelectric Liquid Crystal 12 Layered Structure

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hidehito Iizaka 3-3-5 Yamato, Suwa-shi, Nagano Seiko Epson Corporation

Claims (8)

[Claims] 1. A liquid crystal display device in which an alignment treatment for aligning liquid crystals is performed on the surfaces of two substrates sandwiching the liquid crystal, wherein a first alignment layer and a first alignment layer are formed on the substrates. A liquid crystal display device comprising a second alignment layer on which a concavo-convex shape controlled to align liquid crystal in a desired direction is formed. 2. The liquid crystal display element according to claim 1, wherein the uneven shape is controlled by applying an electric field or a magnetic field to the liquid crystal layer when forming the second alignment layer. 3. In a liquid crystal display element, wherein the alignment treatment for aligning the liquid crystal is performed on the surfaces of two substrates sandwiching the liquid crystal, a first alignment layer is previously formed on the substrate, and A method for manufacturing a liquid crystal display device, wherein a second alignment layer is formed on the polymer layer by polymerizing a polymer precursor previously mixed in liquid crystal. 4. The polymer precursor is polymerized while applying an external field to the liquid crystal layer so that the liquid crystal layer has a desired pretilt when the second alignment layer is formed. The method for manufacturing a liquid crystal display element according to claim 3. 5. The method of manufacturing a liquid crystal display device according to claim 3, wherein the external field is an electric field or a magnetic field. 6. The method of manufacturing a liquid crystal display device according to claim 3, wherein the first alignment layer has a vertical alignment force, a horizontal alignment force, or an alignment force that causes pretilt. 7. The method for manufacturing a liquid crystal display device according to claim 3, wherein ultraviolet light, electron beam or visible light is used to polymerize the polymer precursor. 8. The liquid crystal is mixed with a substance that absorbs ultraviolet rays, electron beams or visible light.
A method for producing the liquid crystal display element described.